This instructable shows you how to make a really nice softbox out of a silvered umbrella. The total project cost was about $23, which is a lot less than any professional model.
So this buddy of mine has a really cool 26″ softbox (Wescott Apollo) that is unique in that it has an internal umbrella shaft and can be used with an ordinary lightstand and speedlight, without any additional hardware. So these softboxes are great, except they cost $140 USD so I set out to make something similar for $23 and it works like a champ! I also wanted something that looked at least sort-of professional, was collapsable and fully portable.
Learn how to make a Softbox from an umbrella
How-To – Super softbox